change employee ID to email address format in exchange online

[Kumton Suttiraksiri]

Dear Expert

My business requirements is that users need to able to sign-in to Office 365 using UPN with email address format. Currently, their username is the <EmployeeID>@emailaddressDomain.com.

A customer has Azure ADConnect. Do you have the suggested solution to do it? 

will Outlook configuration change?

[#2]

This is something you can do with PowerShell:
$Office365Cred=Get-Credential
Connect-MsolService -Credential $Office365Cred
set-msoluserprincipalname -newuserprincipalname <new_user_principal_name> -userprincipalname <Old_UserPrincipalName>

[#3]

How about Azure AD Connect and Outlook configuration?

[#4]

Hi Kumton,

First of all you have to change the UPN in your On-Premises AD, then do a sync.

After you change the UPN like Juan said, your users have to use new UPN format to login and to Outlook reconfigure the profile.

Note: After you change your UPN services like Skype for Business their login and SIP will change to the new one.